Sonochemistry involves the application of ultrasound energy to carry out chemical reactions and processes. The mechanism causing sonochemical effects in liquids is the phenomenon of ultrasonic cavitation. There are many chemical reactions that are influenced by ultrasonic cavitation and that influence can alter the speed and yield of finished products.
There also exists a great quantity of chemical reactions that beneficially proceed under the influence of ultrasonic cavitation. Similar reactions may be accomplished in aqueous, as well as non-aqueous, liquids. Chemical action can occur in the cavitation bubble collapse when there is significant compression heating of the vapor and gas. (Timothy J. Mason, “Advances in Sonochemistry”, Volume 3. 1993. 292 pp., JAI Press Inc.). As the cavitation bubble accelerates through the collapse, no heat is lost through the bubble interface in the final collapsed stage. Though no heat is lost with respect to the amount stored (adiabatic process), there is vigorous heat flux for a brief instant and a thin thermal boundary layer forms near the bubble interface. Experimental results have shown that these bubbles have temperatures around 5000 K, pressures of roughly 1000 atm, and heating and cooling rates above 1010 K/s (K. S. Suslick, Science, Vol. 247, 23 Mar. 1990, pgs. 1439-1445). These high temperatures and pressures can create extreme physical and chemical conditions in otherwise cold liquids.
The following sonochemical effects can be observed in chemical reactions and processes: increase in reaction output and speed, changing of reaction pathway and increase in the reactivity of reagents or catalysts, improvement of phase transfer and activation catalysts, avoidance of catalysts and breakage molecular bonds, improvement of particle and droplets formations and synthesis.
Common for sonochemical reactions and processes is that, for the creation of cavitation bubbles in a liquid, application of ultrasonic oscillations on the liquid is used. The basic equipment which is used in sonochemistry appears as ultrasonic devices of various designs.
This method of conducting sonochemical reactions is sufficiently effective for processing small volumes of liquids and has found its chief application on the level of laboratory research. Transitioning to large scale volumes, however, which are used in industry, is significantly difficult and even at times impossible. This is associated with the problems which arise during the scaling up of cavitation that is produced with the aid of ultrasonic oscillations.
It is possible to avoid these shortcomings, however, by producing the quality of the initiator of sonochemical reactions, cavitation bubbles, through the course of hydrodynamics. An example of using hydrodynamic cavitation for conducting sonochemical reactions is presented in the work of: Pandit A. B., Moholkar V. S., “Harness Cavitation to Improve Processing,” Chemical Engineering Progress, July 1996, pgs. 57-69.
Methods disclosed in U.S. Pat. Nos. 5,937,906; 6,012,492 and 6,035,897, for conducting sonochemical reactions and processes using in large scales liquid medium volumes, involve passing a hydrodynamic liquid flow at a velocity through a flow through channel internally containing at least one element to produce a local constriction of the hydrodynamic liquid flow. The velocity of the liquid flow in the local constriction is at least 16 msec. A hydrodynamic cavitation cavern is created downstream of the local constriction, thereby generating cavitation bubbles. The cavitation bubbles are shifted with the liquid flow to an outlet from the flow through channel and the static pressure of the liquid flow is increased to at least 12 psi. The cavitation bubbles are then collapsed in the elevated static pressure zone, thereby initiating the sonochemical reactions and processes.
The existing methods are not sufficient to generate significant compression energy release during bubble collapse.
The compression of the bubbles during cavitation in the discourse patents occurs under static pressure P1 increased in the liquid flow. Increasing static pressure of the liquid flow is a linear process and pressure cannot be higher than P1>0.3 P (to avoiding cavitation suppression), where P is the static pressure before local constriction which passes a hydrodynamic liquid flow through a flow-through local constriction, and P1 is the static pressure behind local constriction. In most cases cavitation bubbles collapse when static pressure surrounding the bubble is P1=(0.05-0.1) P.
The power output, N, from the cavitation bubble collapse is
      N    =          4.60      ⁢                          ⁢              R        2            ⁢                                    P            1            2                    ρ                      ,where R—maximum radius the bubble has at the beginning of collapse, P1—is hydrostatic external pressure surrounding the bubble, ρ—liquid density.
There are different approaches to account for the shockwave produced from a cavity collapse to, but an approximate relationship for the pressure peak amplitude, pp, given by Brennan is pp=100 RP1/r, where R—is the maximum bubble radius, r—is the distance from the bubble, and P1− is hydrostatic external pressure surrounding the bubble. (C. E. Brennan. Cavitation and Bubble Dynamics. Oxford University: New York, 1995.)
Thus, utilization of static pressure P1 in the liquid flow for compression of the bubbles is not an effective method and leads to a low intensity of sonochemical reactions and decrease the degree of heating the medium. Accordingly, there is a continuing need for alternative methods for realizing sonochemical reactions which can provide more effective utilization energy of the hydrodynamic flow. The present invention contemplates a new and improved method for conducting sonochemical reactions and processes and allows the utilization of more effective hydrodynamic cavitation regimes.